The present invention relates to a universal joint, and more particularly to an improvement on a variable speed type universal joint available for being operated under a relatively small offsetting angle and eccentricity.
A compact variable speed type universal joint capable of being used under an eccentrical condition and eccentrical angle is generally referred to as a hook or Cardan joint. Such a conventional universal joint includes a pair of joint bodies each provided with a yoke, and a coupling member or a spider having a cruciform configuration for coupling together the joint bodies. For this, the coupling member is provided with pins which constitute, in combination, the cruciform shape, and these pins extend through and are slidingly engageable with the yokes.
Japanese Patent Application Kokai No. 62-110630 discloses such a conventional universal joint as shown in FIG. 1. According to the conventional structure, a coupling member 15 includes a rectangular segment 16 and four pins 17 those being separate from the rectangular segment and fixable thereto. Further, joint bodies 11 and 21 include hub portions 11a, 21a, and yoke pieces 13,13 and 23, 23 those formed with holes and separate from the hub portions and fixable thereto by bolts 20. For assembly, firstly, the four pins 17 are fixedly secured to the rectangular segment 16 so as to constitute the coupling member 15 having cruciform shape, and then, the holes of the yokes 13,13 and 23 23 are engaged with the pins 17. Thereafter, the yokes 13, 13 and 23, 23 are fixedly secured to the hubs 11a, 21a by the bolts 20. Sleeve members (not shown) may be interposed between the pins 17 and holes of the yokes 13, 23.
With the above conventional arrangement, after the pins 17 are secured to the rectangular segment 16, the pins 17 must undergo grinding for providing smooth sliding contact with the holes of the yokes, since the pins may be deformed at the time of fixing work to the rectangular segment. However, the intricate machining may be required, and it would be rather difficult to obtain high dimensional accuracy, which then leads to increase in production cost. Furthermore, the yokes 13 13 and 23 23 are initially separate from the hubs 11a and 21a, and therefore, minute assembly error may result. If the fixing between the hubs and the yokes is made with a minute dimensional error, the inherent power transmitting function of the universal joint may be degraded. To avoid this, fine surface accuracies are required at surface engagement portions of the yokes and hubs, and thread holes formed in the hubs and yokes for engagements with the bolts 20 must also provide high accuracy. Accordingly production cost of the joint bodies 11 and 21 may be increased.